Grayscale YUV rpi

gray_yuv.c

    //Try to some colors http://en.wikipedia.org/wiki/YUV
    int chrominance_offset = userdata->width * userdata->height;
    int v_offset = chrominance_offset / 4;
    int chroma = 0;
    
    if (output_buffer) {
        mmal_buffer_header_mem_lock(buffer);
        memcpy(output_buffer->data, buffer->data, buffer->length);
        
        int grayOffset;
        for (grayOffset = chrominance_offset; grayOffset < (chrominance_offset + v_offset + v_offset); ++grayOffset)
        {
            output_buffer->data[grayOffset] = 0x00;
        }

        /*
        // dim
        int x, y;
        for (x = 0; x < 600; x++) {
            for (y = 0; y < 100; y++) {
                if (local_overlay_buffer[(y * 600 + x) * 4] > 0) {
                    //copy luma Y
                    output_buffer->data[y * userdata->width + x ] = 0xdf;
                    //pointer to chrominance U/V
                    chroma= y / 2 * userdata->width / 2 + x / 2 + chrominance_offset;
                    //just guessing colors 
                    output_buffer->data[chroma] = 0x38 ;
                    output_buffer->data[chroma+v_offset] = 0xb8 ;
                }
            }
        }
        */

        output_buffer->length = buffer->length;
        mmal_buffer_header_mem_unlock(buffer);
        if (mmal_port_send_buffer(userdata->encoder_input_port, output_buffer) != MMAL_SUCCESS) {
            fprintf(stderr, "ERROR: Unable to send buffer \n");
        }
    } else {
        fprintf(stderr, "ERROR: mmal_queue_get (%d)\n", output_buffer);
    }